After much effort I am 90% sure that the new disc brakes have been bled properly. Using the Phoenix injector was the final fix for me.

However, it was 3-4 years ago when I installed the new booster and MC. The pedal is not spongy at all. But when the car is running, the pedal goes all the way to the floor before the brakes engage. I wonder if having installed the shorter push rod would cause this, or would they even engage? I seem to remember installing the shorter push rod (the one on the MC side) but I can't remember for sure.